Ratio of binding energy of a nonrotating 18 M _⊙ model (left) or of our 15 → 18 M _⊙ accretor (right) divided by the binding energy of the rotating models of Figure 7. The binding energy includes the internal energy (α _th = 1); the gray bands highlight the CEB region of the models in the numerator. Lighter colors indicate ratios to an initially faster-rotating single star; see also legend in Figure 7.